STMicroelectronics STM32F05 series Reference Manual page 489

RM0091
Table 66. I2C-SMBUS specification clock timings (continued)
Symbol
Bus free time between a
t
BUF
STOP and START condition
t
Low period of the SCL clock
LOW
t
Period of the SCL clock
HIGH
Rise time of both SDA and SCL
t
r
signals
Fall time of both SDA and SCL
t
f
signals
Note: SCLL is also used to generate the
SCLH is also used to generate the
Refer to
I2Cx_TIMINGR settings vs. I2CCLK frequency.
Master communication initialization (address phase)
In order to initiate the communication, you must program the following parameters for the
addressed slave in the I2Cx_CR2 register:
●
Addressing mode (7-bit or 10-bit): ADD10
●
Slave address to be sent: SADD[9:0]
●
Transfer direction: RD_WRN
●
In case of 10-bit address read: HEAD10R bit. HEAD10R must be configure to indicate
if the complete address sequence must be sent, or only the header in case of a
direction change.
●
The number of bytes to be transferred: NBYTES[7:0]. If the number of bytes is equal to
or greater than 255 bytes, NBYTES[7:0] must initially be filled with 0xFF.
You must then set the START bit in I2Cx_CR2 register. Changing all the above bits is not
allowed when START bit is set.
Then the master automatically sends the START condition followed by the slave address as
soon as it detects that the bus is free (BUSY = 0) and after a delay of t
In case of an arbitration loss, the master automatically switches back to slave mode and can
acknowledge its own address if it is addressed as a slave.
Note: The START bit is reset by hardware when the slave address has been sent on the bus,
whatever the received acknowledge value. The START bit is also reset by hardware if an
arbitration loss occurs. If the I2C is addressed as a slave (ADDR=1) while the START bit is
set, the I2C switches to slave mode and the START bit is cleared when the ADDRCF bit is
set.
Note: The same procedure is applied for a Repeated Start condition. In this case BUSY=1.
Parameter
Section 23.4.10: I2Cx_TIMINGR register configuration examples
Doc ID 018940 Rev 1
Inter-integrated circuit (I
Standard Fast Mode
Min Max Min Max
4.7 1.3
4.7 1.3
4.0 0.6
1000 300
300 300
t and t timings.
BUF SU:STA
t and t timings.
HD:STA SU:STO
2
C) interface
Fast Mode
SMBUS
Plus
Min Max Min Max
0.5 4.7
0.5 4.7
0.26 4.0 50
120 1000
120 300
for examples of
.
BUF
Unit
µs
µs
µs
ns
ns
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